sec.rcode0.net has no MX records.
Question and response
Question
dig sec.rcode0.net. MX
Answer
The response has no answer records.
Authority
rcode0.net. 600 SOA sec1.rcode0.net. rcodezero.ipcom.at. 2026020400 1200 1200 2419200 600
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0